Wort froze AFTER pitching!

[jmacker]

So I wrapped up a successful brewday utilizing the recirculating immersion chiller method I recently read about here. I kept the chilling water cool with multiple jugs of ice that I had been stockpiling and freezing in my fermentation chamber/chest freezer for the past couple weeks. Seemed to work pretty well given the hot temperatures outside.
I transferred 11 gallons from the garage to the basement using a long transfer hose with a DIY copper pipe venturi at the end into two better bottles at about 80F and figured I'd let the chamber bring it the rest of the way down to pitching temps - as usual.
I pitched a short time later at about 65F with 2 packs of non-rehydrated Nottingham in one and S-04 in the other. This is the Old Speckled Hen clone. My plan was to bring the temp down to 59-60 for fermentation - but I forgot to change the temperature settings from when I used it to freeze the jugs!
I checked the following morning and both better bottles were sort of slushy - not frozen solid.
I have two questions:
Assuming the yeast is dead, can I repitch and forget about it?
Did the freezing affect the oxygenation levels of the wort and if so, what do
I do about that?
Thanks for any input you can offer.

 

[PartagasD4]

I bet if you bring the temp up you will be fine. I don't think yeast die that easily especially if it was not a really hard freeze. I also think your O2 is fine especially with dry yeast.

 

[brandonlovesbeer]

I accidentally froze a beer one time. When I eventually went to bottle it still carbed up fine.

 

[65C]

my experience with yeast (from a lot of bread making) is that it's fine getting icy - but the other way kills it

bring it up to 16C+ and I'm sure it will be fine - maybe keep temps low for a bit for it to adjust

I'm finding yeasts are working fine at much lower temps than advised - and actually work crap at 20C+ - beer tastes like fruit

 

[SlitheryDee]

Just from what I know about storing harvested yeast I'm sure you'll be fine. What they say is that you can harvest yeast and freeze it to retain viability for a very long time, but the ice crystals that form will kill approximately half the yeast, so you have to make a starter from stored yeast before pitching.

In your case, where the yeast never froze solid I would think that you would retain a higher percentage of viable yeast, perhaps nearly all of it. I would expect fermentation to proceed more or less normally once the beer warmed to near the yeast's active temperature range.

 

[Dcpcooks]

I know co2 comes out of suspension in warming conditions, I'd suspect o2 is the same. So I doubt o2 is a concern. It's probably at the same level it was going into the fermentor.

As to your yeast, all liquid yeast is stored at around 32-42 degrees so I highly doubt you killed it as you didn't freeze it solid. The concern with freezing isn't necessarily the freezing temps but rather the fact that most freezers warm and cool slightly over time. That causes ice crystals to form which rupture the cell walls and kill the yeast. That's also what freezer burn with any cellular protein or plant matter.

You will experience a longer than usual lag time. It may be as long as four days if my memory serves me. You can look up yeast cycles in the "yeast" book to confirm or with google if you desire.

So if you've got good sanitary cleaning practices I'm sure you'll be fine and your yeast will ferment the beer. If you've got less than good sanitation you may have allowed enough lag time for a bug to take hold and get started. Consider the fact that you still have more yeast than potential spoilage bugs I'd suspect you'll be fine. I would ramp your temps up slowly to the low end of the yeast temp range over a day or so and keep the fermentor closed. If you don't see any signs of a krausen in three or four days I'd repitch.

Remember that as the wort warms you may see some off gassing in the airlock so don't use the airlock as a gauge of fermentation.

 

[jmacker]

Thanks everyone for the reassurances. I set the temp to 16C on Friday before leaving town. Got home this afternoon and there was a healthy krausen on both. Big relief!